A variety of means were used to get wounded men to where they could be treated. This gallery contains images of many of those means of conveyance--including light rail tramways, horse drawn carts, and ambulance trucks.
Casualty clearing stations were typically located near rails and main roads and were as close to the front as was safe. The seriously wounded were taken to a casualty clearing station to be given emergency medical attention. Men who needed further medical attention were then typically loaded on trains to be taken to either a stationary hospital or a hospital ship.
Field ambulance is a term that was used by the British and Dominion armies to refer to a mobile medical unit that treated wounded soldiers very close to the combat zone. It was one level up from an advanced dressing station.